The question of how meals influence the level of blood glucose (also referred to as blood sugar) in diabetics is of high medical relevance. This is reflected for example by the fact that professional medical associations such as the IDF (International Diabetes Foundation) or the ADA (American Diabetes Association) have published guidelines on this topic (see for example http://www.idf.org/webdata/docs/Guideline_PMG_final.pdf or http://care.diabetesjournal.org/cgi/reprint/31/Supplement_1/S12.
The ingestion of meals or carbohydrates is the most important influencing factor for an increase of blood glucose in type 1 and type 2 diabetes. Increased levels of blood glucose are the most important factor for late complications of diabetes such as kidney failure, blindness, myocardial infarction, amputations, etc. However, the determination of the meal-related increase in blood glucose for the individual in relation to the main meals has not been adequately addressed.
Experimental tests such as GCT (Glucose Challenge Test) or OGTT (Oral Glucose Tolerance Test) are methods for determining the increases in blood glucose in which the patient ingests a defined amount of glucose and the blood glucose is determined before and at defined times after the ingestion. These tests can only be carried out under defined conditions in professional facilities, and they are time-consuming and stressful for the patient. Furthermore, these tests are carried out generally without the effect of anti-diabetic therapeutic agents.
Of medical relevance and interest is the effect of various meals on the blood glucose under the typical medication of the patient. This can be used as a basis to determine whether the type of medication, and dose and time of administration are suitable for keeping post-prandial blood glucose increases within certain limits.
The self-measurement of blood glucose is in principle a very suitable method for quantifying the said effects. However, certain boundary conditions have to be adhered to and checked in order to ensure the validity of the measured values.
In this connection it is important to accurately assign blood glucose values to a meal. In particular a measurement must be carried out immediately before the meal, another measurement must be carried out within a certain time frame after the meal and typically between 1 and at most 2 hours after the meal. Furthermore, several pairs of measurements for different days at different meal-times or times of days should be present in order to make statistically sound statements about the changes in blood glucose at various meal-times.
Apart from the above-mentioned clinical tests GCT and OGTT, only the self-measurement of blood glucose values is available at present. The measured values can then for example be recorded in diabetes diaries. These diaries often have categories such as “before breakfast” and “after breakfast” in which the measured values are then recorded and can be examined by the doctor. However, it is known from the literature that a high percentage (>50%) of the manually recorded blood glucose values are incorrect and incomplete (cf. e.g. Reliability of self-recorded blood glucose data in patient logbooks compared with SMBG data saved in device memory and printed out with Accu-Chek Smart Printer; J. K. Tshiang Tshiananga, D. Franke, M. Luebker, C. Weber, K. Neeser, 43rd EASD (2007) Annual Meeting, Amsterdam). Moreover, it is not possible to ascertain whether the time criteria for the measurements have been correctly adhered to. Furthermore, an evaluation of several measurement events is difficult to carry out and equally susceptible to error.
As an alternative the blood glucose values can be read out of the memory of the blood glucose measuring instrument and analyzed with appropriate software programs. Some blood glucose measuring instruments also allow individual values to be labeled as pre-prandial or post-prandial (i.e. in this connection as “before” or “after” a meal).
These software evaluations are usually based on arranging the stored measurements in various meal classes on the basis of the time of measurement. If the meal class “before breakfast” is for example defined as 5:30 am to 8:00 am, a value measured at 5:32 am is automatically assigned to this meal class. In some cases technical solutions are offered in which a measurement can be directly assigned to a certain meal class depending on the time.
The majority of the available software programs calculate average blood glucose values and spread (e.g. standard deviation or range) for the various meal classes.
The disadvantage of the existing solutions is that the type of statistic treatment of the measured blood glucose values could lead to an erroneous interpretation of the meal-related blood glucose differences.
Calculation of the isolated statistics for the individual meal classes can easily lead to conclusions about the influence of meals on the basis of differences in means between the “before” and “after” values (i.e. the pre-prandial and post-prandial measurements). These can for example be misleading because the “before” measurements have been carried out on different days than the “after” measurements and differences between the values are not due to the ingested meals. Moreover, the fact that a correct chronological sequence of blood glucose measurements in relation to meal ingestion is necessary for a correct determination of the meal-related blood glucose change is usually disregarded.